Apparently it starts moving when it’s filled up, with no particular bus timing.

I reached at about 145pm. When I got off (in Montenegro) there were many people asking where I wanted to go, offering tours to the nearest cities, beach-style resorts around. I walked around and found myself at hotel rozafa, in a bid to steal wifi to google further. somehow, it turned out that there was the spot I was supposed to wait for the bus to Podgorica. Hurray!